1. Field of the Invention
The present invention relates to a dibenzothiophene compound and an organic light-emitting element based on this compound.
2. Description of the Related Art
Organic light-emitting elements have a cathode, an anode, and an organic compound layer located between these two electrodes. The electrodes individually inject holes and electrons into the organic compound layer, which in turn serves as a light-emitting layer where the holes and the electrons are coupled again and form excitons. These excitons then return to their ground state, and light is emitted thereby. There have been great advances in the organic light-emitting element technology in recent years, and now we can fabricate light-emitting devices with a light weight, a low profile, quick responses, various emission wavelengths, and a low driving-voltage requirement.
Organic phosphorescence-emitting elements are another type of organic light-emitting elements, which have a phosphorescence-emitting material in their light-emitting layer, and triplet excitons formed in this material release light.
International Publication Nos. WO 2009-085344, WO 2009-021126, WO 2006-137210, and Japanese Patent Laid-Open No. 2009-267257 (no foreign equivalents available) describe organic light-emitting elements with the following compounds as the host material.

International Publication No. WO 2009-085344 discloses a compound composed of dibenzothiophene and heterocycles introduced at the C4 and C5 positions (Compound SS-1). International Publication No. WO 2009-021126 discloses a compound composed of dibenzothiophene and different aryl substituents at the C4 and C5 positions (SS-2). International Publication No. WO 2006-137210 discloses two compounds composed of dibenzothiophene and a single kind of fused polycycle with the polycycles introduced at the C2 and C7 positions in one and at the C3 and C6 positions in the other (SS-3 and SS-4). And, Japanese Patent Laid-Open No. 2009-267257 discloses a compound having heterocycles with nitrogen-carbon bonds (SS-5).
Unfortunately, however, organic light-emitting elements based on these compounds have only a short operation life.